Subsurface pressure reduction drilling apparatus

ABSTRACT

A pulse generator adapted to be connected to a drill pipe string at its upper end and a drill bit at its lower end, drilling fluid being pumped down through the drill pipe, generator and bit, the generator embodying a pair of shock passages alternately opened and alternately closed by a shuttle valve in the path of drilling fluid flowing into the generator from the drill pipe string, closing of one of the shock passages, which includes the bore hole cavity in which the bit is operating, effecting a reduction in the hydrostatic pressure therein to increase the drilling rate of the bit in the formation.

Chenoweth et al,

SUBSURFACE PRESSUE MEIDUCTFIUN 1 air, M, 1972 3,235,017 2/1966 Lynes ..175l321 DRILLING APPARA'HUfi 3,094,176 6/1963 Cook 3,532,174 10 1970 D' t'd 7 5 [72] Inventors: David V. Chenoweth; 'llae lL. Crone, lamanl es 1 5/ 6 both of Houston Primary Examiner.lames A. Leppinls [73] Assignee: Baker Oil Tools, lnc., Commerce, Calif. A"meyBemmd Knegel [22] Filed: Feb. 19, 1970 [57] ABSTRACT [2]] Appl. No.: 12,591 A pulse generator adapted to be connected to a drill pipe v string at its upper end and a drill bit at its lower end, drilling fluid being pumped down through the drill pipe, generator and il ..1l75/56, l75l232zlli7ggfig bit, the generator embodying a pair of Shock passages [58] i 232 234 temately opened and alternately closed by a shuttle valve in 17543 1 6, 8 the path of drilling fluid flowing into the generator from the drill pipe string, closing of one of the shock passages, which ineludes the bore hole cavity in which the bit is operating, ef- [56] References cited fecting a reduction in the hydrostatic pressure therein to in- UNITED STATES PATENTS crease the drilling rate of the bit in the formation.

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197' ra/vea m SUBSUIRIFACE PRESSURE REDUCTIIUN DRILLING APPARATUS The present invention relates to subsurface bore hole apparatus, and more particularly to apparatus employed in the drilling of bore holes, such as oil and gas wells.

In the drilling of a well bore, circulating fluid is pumped down through a string of drill pipe, discharging from the drilling bit attached to its lower end for the purpose of cleaning and cooling the drill bit and flushing the cuttings from the bottom of the hole and upwardly around the drill pipe string to the top of the bore hole. As the depth of the bore hole increases, the hydrostatic pressure of the fluid therein also increases, such pressure being imposed upon the formation, including the region of the formation at which the drill bit is operating. Hard formations may have a brittle nature when subjected to comparatively low confining (hydrostatic) fluid pressure, but they achieve a ductile nature at relatively high confining (hydrostatic) pressures. When the bit is operating upon a formation having a relatively brittle nature, it produces comparatively large chips or fragments, but such size of chips or fragments is not achieved when the formation has ductile characteristics. Where the hydrostatic head or pressure of the fluid is high, the chips formed by the drill bit may remain coherent to the formation mass. As a result, the drilling fluid pumped down the drill string and discharging from the bit cannot effect rapid chip removal, which results in a loss of penetration efiiciency of the drill bit cutting elements.

By virtue of the present invention, a confining (hydrostatic) pressure in the well bore, where the drill bit is operating, is decreased. An apparatus is provided that produces a very abrupt rise and fall in pressure in the well bore at the location of the bit. The apparatus includes a shock tube or passage oscillator arrangement, in which the moving fluid through the apparatus is caused to produce a negative pressure in such passage which includes the well bore cavity in which the bit is operating, thereby resulting in the formation retaining its brittle nature and effecting increased drilling rate or efficiency because of the fact that the bit produces larger formation chips. In addition, the abrupt intermittent rise and fall in pressure developed in the bore hole cavity where the bit is operating produces shock front stress relaxation and buildup at the rock interface, along with near explosive chip spawling characteristics, in the formation, which further enhances the production of chips by the rock bit.

In a more limited sense, the invention contemplates the attachment of a pulse generator to the lower end of a tubular drill string, the lower end of the pulse generator being secured to a drill bit. The pulse generator provides a shock oscillator passage, which includes the region of the bore hole in which the bit is operating, and in which a shuttle valve operates automatically in response to the flow of fluid through the pulse generator and shock passage to intermittently interrupt the flow of fluid to the shock passage, producing a negative pres sure therein which is substantially below the pressure exerted by the hydrostatic head of fluid in the bore hole above the shock passage. Preferably, another shock passage or branch is provided in the pressure pulse generator to achieve hydrostatic counterbalancing, the shuttle valve alternately closing the flow of fluid into the counterbalancing passage and the formation shock passage.

An objective of the invention is to provide an improved apparatus which effects a reduction in the hydrostatic head of pressure in the bore hole where the drill bit is operating, so as to increase its drilling rate or efficiency. Such pressure reduction may be to a value below the formation pressure, which causes the latter to assist in the drilling action of the bit by enhancing the production of chips and their disengagement from the drilling face. The fluid flowing through the apparatus not only achieves the intermittent rise and fall of the hydro static head of pressure in the bore hole at the drilling region, but also performs its normal function of cleaning and cooling the drill bit, and of flushing the cuttings from the drilling region upwardly in the well bore to the top thereof.

A further object of the invention is to provide an apparatus that not only reduces the fluid pressure in the well bore at the location of the rotary drilling bit, but which also applies intermittent impact blows or thrusts on the bit, resulting from the intermittent reduction of the fluid pressure.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not. to be taken in a limiting sense.

Referring to the drawings:

FIG. l is a side elevation of apparatus embodying the invention disposed in a bore hole being drilled;

FIGS. 2a and 2b together constitute an enlarged longitudinal section through the pressure pulse generator portion of the apparatus disclosed in FIG. 1, FIG. 2b being a lower continuation of FIG. 2a;

FIG. 3 is a cross section taken along the line 3-3 on FIG. 21;,-

FIGS. 4a and 41b together constitute a longitudinal section through another embodiment of pressure pulse generator, FIG. 4b being a lower continuation of FIG. 4a;

FIG. 5 is a schematic diagram of the fluid pressure oscillator or pulse generator circuits embodied in the forms of generators disclosed in FIGS. 2a, 2b and 4a, 4b; and

FIG. 6 is a graph illustrating the pressures generated in the bore hole where the drill bit is operating.

In the form of the apparatus illustrated in FIGS. 1 to 3, a drill bit A of any suitable form, such as a roller bit, is secured to the lower end of a pulse generator B, the upper end of which is attached directly to the lower end of a string of drill pipe C, such as to the lower end of a drill collar D, fon'ning part of the drilling string, or to an intervening reamer E adapted to stabilize the apparatus in the well bore, or enlarge the bore hole diameter, or both. If a reamer is used, it may have toothed roller cutters F thereon adapted to enlarge the diameter of the bore hole H.

The pulse generator B includes an upper sub 10 having an upper pin II for threadedly securing it to the adjacent threaded box portion l2 of the reamer E or drill collar C, this sub being threadedly secured to an elongate outer sleeve or housing 13, the lower end of which is threadedly attached to a lower mandrel M having a lower reduced diameter portion 15 piloted within a bit sub 16, which can move longitudinally to a slight extent with respect to the mandrel, but which rotates with the mandrel and transmits drilling torque therefrom because of the provision of a coupling 17 between these two members. Such coupling includes axially directed jaws or teeth IS on the upper portion of the bit sub meshing with companion jaws or teeth 19 on the lower mandrel. Downward movement of the bit sub 16 with respect to the mandrel I4 is limited by engagement of an upper flange 20 on a gauge sleeve 21, surrounding and threadedly secured to the sub 16, with an underlying flange 22 on the lower mandrel, relative upward movement of the bit sub 16 along the mandrel being limited by engagement of an upwardly facing sub shoulder 23 with a downwardly facing shoulder 24 on the mandrel. Fluid leakage between the mandrel and sub is prevented by one or a plurality of side seals 25 mounted in the bit sub 16, slidably and sealingly engaging the periphery of the reduced diameter portion l5 ofthe mandrel 14.

The mandrel 141 also has a lower small diameter section 26 extending into the lower portion of-tl'ne bit sub 16, this lower section and the central portion of the mandrel itself having a fluid passage 27 for delivering fluid into a threaded box 28 at the lower portion of the bit sub, which is adapted to threadedly receive the upper pin 29 of the rotary drill bit A, this drill bit having the usual discharge nozzles (not shown) from which fluid is directed into the bore hole to clean and cool the bit cutters 30 and convey the cuttings upwardly in the bore hole to the top thereof.

Disposed within the housing 13 is an outer shock tube 31, the lower end of which is threadedly secured to the lower mandrel 14, and the upper end 32 of which terminates a short distance below the lower end of the upper sub 10. This outer tube is eccentrically disposed in the outer sleeve 13 for a purpose described hereinbelow, but is in spaced relation to the outer sleeve or housing 13 to provide an eccentric annular passage 33 therebetween, the lower end of this passage communicating with a discharge opening 34 in the lower end of the outer sleeve or housing, and also with a passage 35 in the lower mandrel that has an opening 36 for discharging fluid and cuttings into the bore hole annulus 37 surrounding the outer sleeve immediately above the gauge sleeve 21. A perforated tube or screen 38 is threadedly attached to the lower mandrel 14, extending upwardly into the annulus 33, and which communicates with the mandrel passage 35 to prevent such passage from being plugged by cuttings which will pass primarily out through the discharge opening 34 in the lower portion of the outer housing 13.

A valve seat sub 39 has its lower portion threadedly secured to the lower mandrel 14, extending upwardly therefrom into the outer shock tube 31. A shock tube sub 40 is threadedly attached to the upper portion of the valve seat sub, its upper end being threadedly attached to the lower end of an inner shock tube 41 extending upwardly within the outer shock tube 31, with its upper end 42 terminating a short distance below the lower end of the upper sub 10. The inner shock tube 41 is in spaced relation to the outer shock tube 31, being retained in such relation by one or more screws 43 threaded in the outer shock tube and engaging the exterior of the inner shock tube. Located within the inner shock tube 41 is a flow tube 44 piloted within the upper sub and extending downwardly within the inner shock tube 41 to an extent in which its lower end 45 is disposed above and in spaced relation to an end wall 46 of the valve seat sub 39, the flow tube being secured to the inner shock tube 41 in spaced relation thereto by one or a plurality of upper and lower spacer elements 47 welded to the flow tube 44 and inner shock tube 41. A shuttle valve 48 is disposed within the shock tube sub 40 between the lower end 45 of the flow tube and the end wall 46 of the valve seat sub, being in slidable sealing relation with the inner wall 49 of the shock tube sub. The lower end of the valve is adapted to engage the end wall 46 when in a lower position, and its upper end adapted to engage the lower end 45 of the flow tube 44 when in its upper position.

Fluid pumped downwardly through the drill string C and reamer E enters the passage 50 in the upper sub and can flow downwardly through the flow tube 44. When the shuttle valve 48 is in its lower position sealed against the end wall 46 of the valve seat sub 39, the fluid flows upwardly through the annular space 51 between the flow tube 44 and the inner shock tube 41, discharging from the upper end 52 of such annular space into the upper portion of the outer housing 13, and then flowing downwardly therethrough through the annular space 33 between the outer shock tube and housing for discharge from the opening 34 provided in the lower portion ofthe outer housing or sleeve and through the discharge opening 36 of the mandrel 14. When the shuttle valve 48 is in its upper position seating and sealing against the lower end 45 of the flow tube. the fluid cannot flow into the annular space 51 between the flow tube and inner shock tube. Instead, it passes downwardly through the central passage 53 of the shuttle valve 48 and into an annular space 54 provided between the reduced diameter upper portion 55 of the valve seat sub 40, and then through side ports 56 in the latter into the central passage 57 through the sub, the fluid then flowing downwardly through the mandrel passage 27 into the drill bit A, discharging therefrom into the bore hole cavity K in which the drill bit is located.

As described hereinbelow, the gauge sleeve 21 and elements mounted thereon make a close sealing fit with the wall L of the well bore, so that the fluid discharging from the drill bit will pick up the cuttings produced by the bit A and convey them upwardly around the bit and the lower portion of the bit sub 16, passing through inlet ports 58 in the bit sub and into an annular space 59 provided between the bit sub and the reduced diameter portion 26 of the mandrel, the fluid and cuttings then passing upwardly through one or more longitudinal passages 60 in the bit sub which open into the annular space 61a between the valve seat sub 39 and the mandrel 14, which communicates with the annular space 61 between the inner and outer shock tubes or sleeves 41, 31, the fluid and cuttings discharging from the upper end of such annular space into the outer housing 13, and then passing downwardly through the annular space 33 between the outer housing and outer shock tube 31 to the discharge openings 34, 36, passing outwardly therefrom into the bore hole annulus 37 surrounding the outer housing, moving upwardly therethrough and through the annulus surrounding the drill string C to the top of the bore hole.

In the specific form of apparatus illustrated in the drawings,

' the bore hole cavity K in which the drill bit A is operating is isolated from the bore hole M above the gauge sleeve 21, so that reduction in pressure is achieved in the bore hole cavity in which the bit is operating to a value substantially below the fluid pressure in the well bore above the cavity, to increase the drilling rate of the drill bit. Such isolation is achieved by securing reaming cutter elements 65, such as tungsten carbide inserts, on the lower portion of the gauge sleeve 21, which are adapted to ream and increase the diameter of the bore hole to a slight extent over the bore hole diameter drilled by the bit A, such cutter elements producing a small annular shoulder 66 in the formation. To effect a further seal with the formation, the upper portion of the gauge sleeve may have tungsten carbide 67 welded thereon, which will also engage the wall of the well bore. Thus, the lower tungsten carbide inserts 65 and the upper sleeve of tungsten carbide 67 welded on the gauge sleeve isolate the fluid under pressure in the bit cavity K from the fluid under pressure in the annulus 37 surrounding the housing 13 above the gauge sleeve 21.

By way of example, the annular passage 51 between the flow tube 44 and inner shock tube 41 may have a length of about 18 feet. When the shuttle valve 48 is in its lower position engaging the valve seat 46, fluid can flow from the flow tube upwardly into this annular passage, discharging from the upper end of the latter. This annular passage 51 forms one leg of a fluid oscillator circuit. When the shuttle valve 48 is in its upper position engaging the lower end 45 of the flow tube 44 and preventing fluid from passing into the annular passage 51 just referred to, the fluid under pressure flows through the shuttle valve 48, annular space 54 surrounding the upper portion 55 of the valve seat sub, through the ports 56 and the sub and mandrel passages 57, 27, and through the drill bit passage 27a, flowing therefrom through the bit nozzles into the bore hole K below the gauge sleeve 21, and flowing through the inlet ports 58 into the annulus 59 and upwardly through the mandrel passages 60 into the annulus 61 between the inner and outer shock tubes, discharging from the upper end of this annulus into the housing 13. The path just described provides a second leg of the fluid oscillator circuit. The fluid from both legs of the circuit merge in a reservoir area 70 at the upper ends of the inner and outer shock tubes 41, 31, then flowing downwardly through the annulus 33 between the outer shock tube and housing towards the discharge openings 34, 36.

The shuttle valve reciprocates fairly rapidly between its lower position closing the second leg S of the oscillator circuit and its upper position closing the first leg R of the oscillator circuit, and in so doing creates pressure pulses in both legs. Assuming the shuttle valve 48 to be in its upper position, with the drilling string C and the apparatus depending therefrom rotating and with the proper drilling weight imposed on the drill bit A, fluid pumped down the drilling string passes from the flow tube passage 44a through the shuttle valve 48 and through the ports 56, passage 57, lower mandrel passage 27 and through the drill bit into the bit cavity K, then flowing upwardly through the inlet ports 58, annular space 59, longitudinal passages 60, and inner shock tube-outer shock tube annulus 61 to the upper end of the latter, the cuttings being conveyed with the fluid to the reservoir region 70 at the upper ends of the sleeves 41, 31, and then passing downwardly through the housing annulus 33 surrounding the outer shock tube and through the discharge openings 34, 36.

The shuttle valve 48 moves downwardly into engagement with its companion seat 46 to close the second leg S of the oscillator circuit just described, the moving fluid in such leg creating a negative pressure therein, the negative pulse travelling from the shuttle valve 48 through the entire second leg to the reservoir, and then reversely through the second leg back to the shuttle valve, where the pressure achieves a positive value greater than the pressure of the fluid flowing downwardly through the flow tube 44, such positive pressure acting on the lower surface of the shuttle valve 48 to shift it upwardly against the seat 45 at the lower end of the flow tube 44, shutting off flow of fluid through the second leg of the oscillator circuit and permitting fluid to then flow through the open first leg R of the oscillator circuit. The sudden closing of the first leg of the oscillator circuit causes the fluid moving upwardly therethrough to create a negative pressure pulse therein that travels upwardly through the first leg 51(R) to the reservoir 70, and then downwardly therethrough to the shuttle valve 46, where the pressure rises suddenly or abruptly to a value exceeding the fluid pressure below the shuttle valve, act ing on the upper surface of the shuttle valve and effecting a sudden downward shifting of the shuttle valve back into engagement with its valve seat 46 to shut off the flow of fluid through the second leg S of the oscillator circuit, which again I has its reduced pressure pulse travel throughout its entire length to the reservoir 70 and then back again, effecting a reduction in the pressure in the bit cavity K which will be sub stantially below the hydrostatic pressure of the fluid in the well bore.

The foregoing cycle of operation is repeated, the shuttle valve 48 alternately opening and closing each leg of the circuit and producing characteristic pressure waves in the second leg S, which are depicted in FIG. 6. As shown therein, pressure is plotted against time, the hydrostatic pressure of the drilling mud or other fluid being indicated by the line '75, and the formation pressure where the drill bit is operating, being designated by the line 76. The pressure in the second leg ofthe oscillator circuit is designated by the generally rectangular wave 77, the curve depicting more than one cycle of operation. Thus, the upper horizontal line 78 indicates the pressure of the fluid flowing through the second leg S of the oscillator circuit when the shuttle valve 48 is in its upper position. When this valve is shifted by the travelling pressure wave in the first leg R downwardly to close the second leg S, the pressure in the second leg drops suddenly to a value substantially below the hydrostatic pressure of the fluid column in the well bore and, preferably, to a value lower than the formation pressure 76 in the bore hole cavity in which the drill bit is to operate, the lower or negative pressure value being indicated by the lower horizontal portions 78 of the curve. When the travelling wave in the second leg S returns to the shuttle valve 46 and shifts it upwardly, the pressure flowing through the second leg is suddenly restored to its upper value 78 above the value 75 of the hydrostatic head of fluid in the bore hole, so that the circulating fluid can carry the cuttings upwardly with it to the top of the bore hole.

The pulse generator or fluid oscillator B provides very rapid low pressure pulses in the cavity K below the gauge sleeve 21 in which the drill bit A is operating. For example, the frequen cy of operation of the shuttle valve may range from about to about 40 cycles per second. The result is a great reduction ofthe hydrostatic pressure at the drill bit A, without the necessity for reducing the hydrostatic head of the drilling fluid in the well bore above the pulse generator apparatus As a result, the formation material in the drilling region retains its brittle nature, breaking down under the action of the drill bit cutters 36 which produce larger rock chips or fragments. In the event that the pulse generator is designed and operated so as to produce negative pulses in the second leg 5 below the formation or rock pressure 76, then the latter will also assist the drilling action by creating an implosion, facilitating breaking down of the brittle formation under the action of the drill bit.

The outer shock tube 31 is disposed eccentrically of the axis of the pulse generator to provide a larger lateral space at one side of the annulus 61, permitting ready passage oflarger drill bit cuttings upwardly therethrough and into the reservoir 70. Such eccentric disposition also provides a larger lateral space at one side of the annular space 33 between the outer shock tube 31 and the housing 13 through which the cuttings can pass downwardly toward the discharge openings 34, 36.

It is to be noted that the bit sub ll6, drill bit A and gauge sleeve 21 make a slidable spline type of connection with the lower mandrel 14, and, therefore, with the housing 13, permitting limited longitudinal movement of the bit sub 16 and bit A relative to the mandrel 14. In the operation of the apparatus, it is rotated through rotation of the drilling string C, reamer E (if used), pulse generator B and drill bit A, with the drilling weight-being transmitted to the bit through the coengaging mandrel and bit sub shoulders 24, 23. Each time a negative pulse travels through the second leg S of the oscillator circuit, a pressure differential is developed across the gauge sleeve 21 and bit sub l6 which acts in a downward direction thereon over the area T between the periphery of the reduced diameter portion 15 of the lower mandrel and the wall L of the slightly enlarged well bore, providing an impact blow on the gauge sleeve and bit sub over this area which is transmitted to the drill bit A, urging its cutters 30 downwardly against the formation. This impact action is delivered at the same frequency as the negative pulses are generated in the second leg S of the oscillator circuit, which, in the example given above, may range from about 10 to about 40 cycles per second. It acts in conjunction with the normal rotary drilling action to further enhance penetration of the cutters 30 into the formation and increase the drilling rate of the bit. This impacting action, coupled with the reduction in the hydrostatic head of the fluid in the bore hole cavity K in which the bit is operating, adds considerably to the drilling rate of the bit in the formation.

In view of the close flt between the gauge sleeve 21 and the wall L of the formation, it may be desirable for the well bore thereabove to have its diameter enlarged to a further extent, so as to facilitate movement of the complete assembly of apparatus into and out of the well bore. The reamer E enlarges the bore hole and provides adequate clearance between the gauge pack sleeve 21 and the enlarged well bore, permitting I the apparatus to be moved longitudinally in the bore hole in a rapid manner without any material interference.

In the event that the rate of flow of the drilling fluid pumped down the tubular drill string C is to be increased to insure the conveyance of the cuttings to the top of the bore hole, and without any necessity for increasing the work done by the pulse generator B, a fluid bypass is provided. A bypass passage 80 extends through the upper flow sub 10 into the reservoir region 70, and may have a choke or orifice 81 in its discharge end to limit the quantity of fluid flowing through the bypass. Thus, the fluid flowing through the bypass 80 commingles with the fluid passing through the pulse generator B and the cuttings to insure conveyance of the cuttings through the annular passage 33 and out of the discharge openings 34, 36 for upward movement through the annulus surrounding the drill string C to the top ofthe bore hole.

In the form of invention illustrated in FIGS. 4a and 4b, the telescopic connection 17 between the lower mandrel l4 and the bit sub 16 is eliminated, so that the feature of impacting of the drill bit against the bottom of the bore hole may not be secured. As illustrated, the lower mandrel and bit sub are combined into a single unit 140, with the drill bit attached to the lower end thereof, the inlet ports 58 from the cavity K in which the bit is operating opening into the annular space 61a surrounding the valve seat 39, this annular space communicating with the annular space 61 between the inner and outer shock tubes 41, 31. In all other respects, the apparatus is virtually the same as in the other form of the invention and operates in the same manner.

Although a spline connection 17 between the sub or mandrel to which the bit A is connected and the upper portion of a mandrel thereabove is not provided in FIGS. 4a, 4b, yet an annular area of the gauge sleeve 21 and mandrel 14a is still subjected to the fluid pressure thereabove in the cuttings discharge passage 33 and the annulus M surrounding the apparatus and the drilling string, which pressure becomes intermittently greater than the pressure in the cavity K in which the drill bit is operating, providing a downwardly directed pressure differential force which tends to impart an impacting action of the drill bit cutters 30 against the bottom of the bore hole. In view of such impacting action, it is possible for proper penetration of cutters into the formation to be secured with a lesser weight of drill collars D in the drill string C. In other words, the drilling weight imposed by the drill string C on the drill bit can be reduced, thereby facilitating the drilling of a straight hole.

In FIG. 5, a schematic circuit is illustrated for reducing the pressure in the bottom portion K of the bore hole and below that of the hydrostatic head of fluid in the bore hole, which circuit is the same as illustrated in the specific forms of invention previously described. Thus, the drilling fluid flows from the drill string into the flow tube passage 44a and alternately into the first or balancing shock tube R, which discharges into the reservoir or bore hole above the pack-off device or gauge sleeve 21 effecting a seal between the mandrel 14 or 14a and the wall L of the bore hole, the fluid also being capable of flowing from the flow tube into the second shock tube or passage S which runs from the shuttle valve 48, disclosed as being of the reed type in FIG. 5, through the cavity K in which the drill bit is operating, and then up through the cuttings passage or shock tube back to the reservoir. The downward flow of fluid through the shock tube at a pressure P, will first divert the shuttle valve 48 into a position closing a first of the shock passages, such as R, causing a negative pressure pulse therein that travels up to the reservoir 70 and then back down to the shuttle valve, the fluid then passing through the second leg, such as S, of the circuit, including the bit cavity K, and then up through the remainder of the other leg to the reservoir. When the negative pulse completes its travel, it engages the shuttle valve and switches it over to close the second shock passage S and open the first shock passage R, causing a negative pressure in the second leg of the shock tube and in the cavity K in which the bit is operating below the gauge pack 21. The pressure wave in the second leg S travels through the second leg to the reservoir 70 and back down to the shuttle valve 48, shifting it back to a position closing the first shock tube, passage or leg R, whereupon variation in the second leg S and in the cavity K in which the drill bit is operating is essentially the same as that depicted in FIG. 6.

We claim:

I. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator adapted to be connected in a tubular drilling string and adapted to be connected at its lower end to a drill bit that drills the bore hole, said generator having a fluid inlet passage adapted to receive fluid pumped from the drilling string, a shock passageway adapted to receive fluid from said inlet passage, said shock passageway including the region in the bore hole at which the drill bit is cutting the formation, and a shuttle valve device in the path of fluid flow through said passage and passageway shiftable by the fluid from the passage and in the passageway between positions alternately closing and opening the inlet to said passageway to generate a negative fluid pressure pulse wave travelling through said passageway, upon each closing of said passageway inlet, between said shuttle valve device and an end of said passageway located substantially above said bore hole region.

2. In apparatus as defined in claim 1; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore' hole thereabove.

3. In apparatus as defined in claim 1; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on the pulse generator and a drill bit connected to its lower end.

4. In apparatus as defined in claim 1; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a lower portion on which the sealing means is provided and connectable to the drill bit and slidably coupled to an adjacent pulse generator portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said passageway.

5. In apparatus as defined in claim 1; said pulse generator having reamer means thereon for enlarging the diameter of the bore hole and for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.

6. In apparatus as defined in claim 1; said pulse generator having reamer means thereon for enlarging the diameter of the bore hole and for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having'a transverse pressure responsive surface subject to the bore hole pressure above said reamer means to exert a downward thrust on the pulse generator and a drill bit connected to its lower end.

7. In apparatus as defined in claim 1; said pulse generator having reamer means thereon for enlarging the diameter of the bore hole and for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a lower portion on which the reamer means is provided and connectable to the drill bit and slidably coupled to an adjacent pulse generator portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said reamer means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave traveling through said passageway.

8. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator adapted to be connected in a tubular drilling string and adapted to be connected at its lower end to a drill bit that drills the bore hole, said generator having a fluid inlet passage adapted to receive fluid pumped from the drilling string, a first shock passageway adapted to receive fluid from said inlet passage, a second shock passageway adapted to receive fluid from said inlet passage and including the region in the bore hole at which the drill bit is cutting the formation, and a shuttle valve device in the paths of fluid flow through said passage and passageways shiftable by the fluid in the passageways alternately between a first position closing the inlet to said first passageway and opening the inlet to said second passageway and a second position opening the inlet to said first passageway and closing the inlet to said second passageway, whereby closing of each inlet generates a negative fluid pressure pulse wave travelling through its associated passageway between said shuttle valve device and an end of said associated passageway located a substantial distance from said inlet.

9. In apparatus as defined in claim 8; said ends of said passageways communicating with each other.

10. In apparatus as defined in claim 8; said ends of said passageways communicating with each other a substantial distance above said bore hole region.

ll. In apparatus as defined in claim 8; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.

l2. In apparatus as defined in claim 8; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on the pulse generator and a drill bit connected to its lower end.

13. In apparatus as defined in claim 8; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a lower portion on which the sealing means is provided and connectable to the drill bit and slidably coupled to an adjacent pulse generator portion for the transmission of torque from said adjacent portion. through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said second passageway.

14. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator comprising an outer structure adapted to be connected at its upper portion to a tubular drilling string and at its lower portion to a drill bit that drills the bore hole, a flow tube within said structure and extending downwardly from the upper portion of said structure, said tube being adapted to receive fluid pumped down the drilling string, a first shock passageway extending upwardly from the lower end ofsaid flow tube and located between said flow tube and structure, a second shock passageway extending from sub stantially the lower end of said flow tube and including the region in the bore hole at which the drill bit is cutting the formation and also extending upwardly along the structure and communicating at its upper end with the upper end of said first shock passageway, and a shuttle valve device between the lower end of said flow tube and the inlets to said passageways shiftable by the fluid in the passageways alternately between a first position closing the inlet to said first passageway and opening the inlet to said second passageway and a second position opening the inlet to said first passageway and closing the inlet to said second passageway, whereby closing of each inlet generates a negative fluid pressure pulse wave travelling through its associated passageway between said shuttle valve device and said upper end of said associated passageway.

l5. In apparatus as defined in claim M; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.

In. In apparatus as defined in claim 14; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a lower portion on which the sealing means is provided and connectable to the drill bit and slidably coupled to an adjacent portion of said structure for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said second passageway.

l7. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator comprising an outer structure adapted to be connected at its upper portion to a tubular drilling string and at its lower portion to a drill bit that drills the bore hole, a flow tube within said structure and extending downwardly from the upper portion of said structure, said tube being adapted to receive fluid pumped down the drilling string, an inner shock tube surrounding said flow tube and providing a first shock passa eway therewith extendin upwardly from the lower end 0 said flow tube, a second 5 ock passageway extending from substantially the lower end of said flow tube and including the region :in the bore hole at which the drill bit is cutting the formation, an outer shock tube in said structure surrounding said inner shock tube and defining therebetween a part of said second shock passageway communicating with each other within said structure, and a shuttle valve device between the lower end of said flow tube and the inlets to said passageways shiftable by the fluid in the passageways alternately between a first position closing the inlet to said first passageway and opening the inlet to said second passageway and a second position opening the inlet to said first passageway and closing the inlet to said second passageway, whereby closing of each inlet generates a negative fluid pressure pulse wave travelling through its associated passageway between said shuttle valve device and the upper outlet of said associated passageway.

18. In apparatus as defined in claim 17; said outer shock tube and structure being laterally spaced from each other to provide a passage for fluid and bit cuttings from said outlets to the bore hole annulus surrounding said structure.

19. In apparatus as defined in claim 17; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.

20. In apparatus as defined in claim 17; said structure having means thereon-for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said structure and a drill bit connected to its lower end.

21. In apparatus as defined in claim 17; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a lower portion on which the sealing means is provided and connectable to the drill bit and slidably coupled to an adjacent structure portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said second passageway.

22. In apparatus as defined in claim I4; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said structure and a drill bit connected to its lower end. 

1. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator adapted to be connected in a tubular drilling string and adapted to be connected at its lower end to a drill bit that drills the bore hole, said generator having a fluid inlet passage adapted to receive fluid pumped from the drilling string, a shock passageway adapted to receive fluid from said inlet passage, said shock passageway including the region in the bore hole at which the drill bit is cutting the formation, and a shuttle valve device in the path of fluid flow through said passage and passageway shiftable by the fluid from the passage and in the passageway between positions alternately closing and opening the inlet to said passageway to generate a negative fluid pressure pulse wave travelling through said passageway, upon each closing of said passageway inlet, between said shuttle valve device and an end of said passageway located substantially above said bore hole region.
 2. In apparatus as defined in claim 1; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.
 3. In apparatus as defined in claim 1; said pulse generator having means thereon for sealinG against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on the pulse generator and a drill bit connected to its lower end.
 4. In apparatus as defined in claim 1; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a lower portion on which the sealing means is provided and connectible to the drill bit and slidably coupled to an adjacent pulse generator portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said passageway.
 5. In apparatus as defined in claim 1; said pulse generator having reamer means thereon for enlarging the diameter of the bore hole and for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.
 6. In apparatus as defined in claim 1; said pulse generator having reamer means thereon for enlarging the diameter of the bore hole and for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a transverse pressure responsive surface subject to the bore hole pressure above said reamer means to exert a downward thrust on the pulse generator and a drill bit connected to its lower end.
 7. In apparatus as defined in claim 1; said pulse generator having reamer means thereon for enlarging the diameter of the bore hole and for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a lower portion on which the reamer means is provided and connectible to the drill bit and slidably coupled to an adjacent pulse generator portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said reamer means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave traveling through said passageway.
 8. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator adapted to be connected in a tubular drilling string and adapted to be connected at its lower end to a drill bit that drills the bore hole, said generator having a fluid inlet passage adapted to receive fluid pumped from the drilling string, a first shock passageway adapted to receive fluid from said inlet passage, a second shock passageway adapted to receive fluid from said inlet passage and including the region in the bore hole at which the drill bit is cutting the formation, and a shuttle valve device in the paths of fluid flow through said passage and passageways shiftable by the fluid in the passageways alternately between a first position closing the inlet to said first passageway and opening the inlet to said second passageway and a second position opening the inlet to said first passageway and closing the inlet to said second passageway, whereby closing of each inlet generates a negative fluid pressure pulse wave travelling through its associated passageway between said shuttle valve device and an end of said associated passageway located a substantial distance from said inlet.
 9. In apparatus as defined in claim 8; said ends of said passageways communicating with each other.
 10. In apparatus as defined in claim 8; said ends of said passageways communicating with each other a substantial distance above said bore hole region.
 11. In apparatus as defined in claim 8; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.
 12. In apparatus as defined in claim 8; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on the pulse generator and a drill bit connected to its lower end.
 13. In apparatus as defined in claim 8; said pulse generator having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said pulse generator having a lower portion on which the sealing means is provided and connectible to the drill bit and slidably coupled to an adjacent pulse generator portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said second passageway.
 14. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator comprising an outer structure adapted to be connected at its upper portion to a tubular drilling string and at its lower portion to a drill bit that drills the bore hole, a flow tube within said structure and extending downwardly from the upper portion of said structure, said tube being adapted to receive fluid pumped down the drilling string, a first shock passageway extending upwardly from the lower end of said flow tube and located between said flow tube and structure, a second shock passageway extending from substantially the lower end of said flow tube and including the region in the bore hole at which the drill bit is cutting the formation and also extending upwardly along the structure and communicating at its upper end with the upper end of said first shock passageway, and a shuttle valve device between the lower end of said flow tube and the inlets to said passageways shiftable by the fluid in the passageways alternately between a first position closing the inlet to said first passageway and opening the inlet to said second passageway and a second position opening the inlet to said first passageway and closing the inlet to said second passageway, whereby closing of each inlet generates a negative fluid pressure pulse wave travelling through its associated passageway between said shuttle valve device and said upper end of said associated passageway.
 15. In apparatus as defined in claim 14; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.
 16. In apparatus as defined in claim 14; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a lower portion on which the sealing means is provided and connectible to the drill bit and slidably coupled to an adjacent portion of said structure for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said second passageway.
 17. In pressure reduction apparatus for drilling a bore hole in a formation: a pulse generator comprising an Outer structure adapted to be connected at its upper portion to a tubular drilling string and at its lower portion to a drill bit that drills the bore hole, a flow tube within said structure and extending downwardly from the upper portion of said structure, said tube being adapted to receive fluid pumped down the drilling string, an inner shock tube surrounding said flow tube and providing a first shock passageway therewith extending upwardly from the lower end of said flow tube, a second shock passageway extending from substantially the lower end of said flow tube and including the region in the bore hole at which the drill bit is cutting the formation, an outer shock tube in said structure surrounding said inner shock tube and defining therebetween a part of said second shock passageway communicating with each other within said structure, and a shuttle valve device between the lower end of said flow tube and the inlets to said passageways shiftable by the fluid in the passageways alternately between a first position closing the inlet to said first passageway and opening the inlet to said second passageway and a second position opening the inlet to said first passageway and closing the inlet to said second passageway, whereby closing of each inlet generates a negative fluid pressure pulse wave travelling through its associated passageway between said shuttle valve device and the upper outlet of said associated passageway.
 18. In apparatus as defined in claim 17; said outer shock tube and structure being laterally spaced from each other to provide a passage for fluid and bit cuttings from said outlets to the bore hole annulus surrounding said structure.
 19. In apparatus as defined in claim 17; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove.
 20. In apparatus as defined in claim 17; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said structure and a drill bit connected to its lower end.
 21. In apparatus as defined in claim 17; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a lower portion on which the sealing means is provided and con-nectible to the drill bit and slidably coupled to an adjacent structure portion for the transmission of torque from said adjacent portion, through said lower portion, to the bit connected to said lower portion, said lower portion having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said lower portion and drill bit connected thereto at each negative fluid pressure pulse wave travelling through said second passageway.
 22. In apparatus as defined in claim 14; said structure having means thereon for sealing against the wall of the bore hole to isolate said bore hole region from the bore hole thereabove, said structure having a transverse pressure responsive surface subject to the bore hole pressure above said sealing means to exert a downward thrust on said structure and a drill bit connected to its lower end. 